Radiation-sensitive self-revealing elements and methods of making and utilizing the same

ABSTRACT

Electromagnetic radiation-sensitive elements made essentially of a metallic layer and of an overlayer of an inorganic material capable of interreacting with the metal of the metallic layer, when exposed to electromagnetic actinic radiation, so as to cause a selective etching of the metallic layer surface at the boundary between the metallic layer and the overlayer which is proportional in depth to the amount of exposure to the electromagnetic actinic radiation. The overlayer may be in a solid form as a thin coating adhering to the metallic layer, or it may be in a liquid or a vapor form. Electromagnetic radiation sensitive elements, consisting of a plurality of strata, each made of a pair of layers of dissimilar materials, one of which is metallic and the other is a layer of actinically reactive inorganic material are provided for particular applications. Exposure to actinic electromagnetic radiation of the elements of the invention causes physical and chemical changes in the materials of the two layers resulting in selective removal, after exposure, of some of the materials of predetermined layers for obtaining particular finished articles.

United States Patent Hallman et al.

14 1 Jan. 25, 1972 [72] Inventors: Robert W. Hellman, Utica; Gary W.

Kurtz, Southfield, both of Mich.

[73] Assignee: Teeg Research, Inc., Detroit, Mich.

[22] Filed: July 3, 1969 [21] Appl. No.: 839,038

Related U.S. Application Data 1 in i n-impart of Ser. No. 591,711, Nov. 3, 1966, abandoned.

[56] References Cited UNITED STATES PATENTS 2,841,477 7/1958 Hall ..156/17 X 2,844,493 7/1958 Schlosser... ..96/l.5 2,912,592 11/1959 Mayer 96/1.5 X 2,962,376 11/1960 Schaffert ...,.96/1.5 3,082,085 3/1963 Miller et al. ..96/l.5 3,095,332 6/1963 Ligenza ...96/36.2 X 3,122,463 2/1964 Ligenza et a1. ..156/4 3,170,790 2/1965 Clark ..96/1.5 3,271,180 /1966 White. ..96/36 X 3,312,548 4/1967 Stranghan ..96/1 5 3,317,409 5/1967 Kaspaul et al. 96/l.5 X 3,317,732 5/1967 Deeg ..252/501 X 3,346,384 10/1967 Gaynor ..96/36 Blake ..96/88 Keller et al. ..96/27 FOREIGN PATENTS OR APPLICATIONS 344,354 3/1931 Great Britain 968,141 8/1964 Great Britain 1,151,310 9/1969 Great Britain OTHER PUBLICATIONS Remy, Treatise on Inorganic Chemistry," 1956, Elsevier Publ. Co., pp. 782- 785 Kostyship et al., PhotographicSensitivity Effect in Thin Semiconducting Films on Metal Substrates," Soviet Physics-Solid State, Vol. 8, No.2, Feb. 1966, pp. 45 l- 452 Primary Examiner-George F. Lesmes Assistant ExaminerR. E. Martin Attorney-Hauke, Gifford and Patalidis 57 ABSTRACT Electromagnetic radiation-sensitive elements made essentially of a metallic layer and of an overlayer of an inorganic material capable of interreacting with the metal of the metallic layer, when exposed to electromagnetic actinic radiation, so as to cause a selective etching of the metallic layer surface at the boundary between the metallic layer and the overlayer which is proportional in depth to the amount of exposure to the electromagnetic actinic radiation. The overlayer may be in a solid form as a thin coating adhering to the metallic layer, or it may be in a liquid or a vapor form. Electromagnetic radiation sensitive elements, consisting of a plurality of strata, each made of a pair of layers of dissimilar materials, one of which is metallic and the other is a layer of actinically reactive inorganic material are provided for particular applications. Exposure to actinic electromagnetic radiation of the elements of the invention causes physical and chemical changes in the materials of the two layers resulting in selective removal, after exposure, of some of the materials of predetermined layers for obtaining particular finished articles.

36 Claims, 32 Drawing Figures PATENIEU M2 1 3.631381 32 /2 FIG .5 F 8 36 3,9 35 /z IN-NI. g

FIGJZ INVENTORS ROBERT W. HALLMAN GARY W. KURTZ ATTOR NEYS PATENTEU 2 37 SIIEEI 3K 3 FIG-23 w FIG-2 FIG. 29

s////////////////"///7A\ /Z INVENTORS ROBERT W. HALLMAN GARY W- KURTZ ATTOR N EYS RADIATION-SENSITIVE SELF-REVEALING ELEMENTS AND METHODS OF MAKING AND UTILIZING THE SAME CROSS REFERENCE TO RELATED APPLICATIONS The present application is a continuation-in-part of application Ser. No. 591,711, filed Nov. 3, 1966, now abandoned, and it further includes the subject matter disclosed in copending application Ser. No. 636,864, filed May 8, 1967 now abandoned, and Ser. No. 641,202, filed May 25, 1967, now abandoned.

BACKGROUND OF THE INVENTION As reported in the Soviet Physics-Solid State, Vol. 8, No. 2, Feb., I966, pages 451-452, it is already known that films of some metal halides, and sulfides, such as arsenic selenide and zinc telluride, among others, when deposited on a metal substrate, such as silver, copper, zinc, lead, etc., are capable of giving a visible image, in other words, of exhibiting photosensitivity, under the action of intense incident light. The image becomes visible during the exposure, and there is generally no need of additional processing for revealing the image. Once formed, the image may be preserved for a considerable period of time without fading. For certain materials, the application of heat to the photosensitive elements is necessary in order to reveal or develop the latent image.

The present invention, as will become evident from reading the hereinafter detailed description thereof, constitutes a considerable improvement upon the state of the art as reported by the article hereinabove mentioned In effect, the present invention provides more particularly new methods for obtaining many useful finished articles, such finished articles being obtainable in a much simpler manner than by conventional methods. Utilizing electromagnetic sensitive elements according to the present invention by way of the methods of the present invention, for example lithographic plates, metal engravings of all types, electrical printed circuits, etc., may be obtained.

Briefly stated, the present invention contemplates projecting an image upon an electromagnetic radiation-sensitive element consisting of a layer of silicon or a metallic layer hereinafter designated under the expression metallic layer," disposed or not upon a support backing, the metallic layer being provided with an overlayer of a material or materials exhibiting an affinity for interreacting with the metallic layer when exposed to electromagnetic actinic radiation such as visible light, preferably of a high intensity. The image formed upon the electromagnetic radiation-sensitive element results from interface reactions under the influence of actinic radiation which cause an etching effect upon the surface of the metallic layer in contact with the overlayer, and the interreaction products are subsequently removed chemically or mechanically. If so desired, the unreacted portions of the overlayer may also be removed. The finished article, consequently, consists of the metallic layer presenting at least one surface having selectively etched portions corresponding to the exposed portions and of depths substantially proportional to the amount of illumination or actinic radiation exposure, the unexposed portions remaining intact. The relief image is thus a faithful reproduction of the image projected upon the electromagnetic radiation sensitive element.

If the image projected upon the sensitive element is a highcontrast image, as is the case when the projected image is caused by transparency projection of a model or mask consisting of portions which are capable of transmitting all or almost all of the incident actinic radiation, and other portions which are substantially nontransmissive of such radiation, with appropriate thickness of the metallic layer a complete radiationinduced etching of the metallic layer can be obtained wherever the actinic radiation impinges upon the surface of the ele' ment. Thus, clean edge contoured perforations are obtained through the metallic layer which may, for some applications, be used as such. A potential application, for example, is the manufacture of color registration masks for color kinescopes. In other applications the etched metallic layer may be cemented or bonded, subsequently, to a support backing. If the metallic layer is originally disposed upon a support backing, such as glass, plastic, etc., to which it normally adheres, the finished article has thus an integral support backing without any further processing.

The present invention also contemplates that the materials forming the overlayer of the radiation sensitive elements need not be in a solid phase and are capable of interreacting with the metallic layer when disposed in contact therewith in a liquid phase or in a vapor phase, such interreaction being proportional in effect to the amount of radiation impinging upon the metallic surface. By utilizing such an arrangement, the present invention presents definite advantages for obtaining finished articles in view of the simplicity of the raw materials used in the process and in view of the simple steps in the process. All that is required to practice the method of the present invention is to project an actinic image upon the surface of a metallic plate, foil, or thin-film, in the presence of an inorganic material in a liquid or gaseous form capable of interreacting with the material of the metallic plate, foil or thinfilm under the influence of electromagnetic actinic radiation. This aspect of the present invention greatly simplifies the preparation of radiation sensitive elements, and, in many cases greatly simplifies the steps to be accomplished in order to obtain a usable finished article. The material capable of reacting with the metallic surface being in a liquid or vapor phase does not remain, in most applications, adhering to the metallic surface, the interreaction product may be easily removed by simple mechanical, physical or chemical means, including vaporization or dissolution in the liquid phase during the illumination by actinic radiation and the radiation-sensitive element can be preserved indefinitely without any precautions before exposure as well as after exposure.

The present invention further contemplates providing a multilayer radiation sensitive element, made of a plurality of strata each made of a pair of layers of dissimilar materials capable of actinically reacting with each other, which permits obtaining a relief image corresponding to an original image projected upon the surface of the element and having a substantially greater relief depth than available by means of an element consisting only of two layers of interreacting materials. Every layer is substantially transmissive of the electromagnetic actinic radiation such that the exposure of the element to electromagnetic radiation extends in depth proportionally to the intensity of the actinic radiation. Depending upon the method utilized, according to the present invention, for processing the exposed electromagnetic radiation sensitive multilayer element, the finished article presents a two-level relief image corresponding to and being a reproduction of the original image projected upon the element, or, alternately, the finished article presents a variable depth relief image corresponding to the shape of the image projected on the radiation-sensitive element and varying in depth according to the varied radiation intensity impinged upon the element.

SUMMARY OF THE INVENTION The present invention thus relates to radiation-sensitive elements consisting principally of a pair of separate adhering layers of inorganic materials capable of discretely and selectively interreacting when exposed to discrete and selective exposure to actinic radiation, to methods of preparing such radiation-sensitive element, to diverse structures in which the principle of the invention may be incorporated, and to processes for utilizing the radiation-sensitive elements of the invention for obtaining useful finished articles.

It will be immediately apparent to those skilled in the art that articles obtained by the methods of the present invention have unlimited uses in applications such as, to enumerate a few, photographic twoand three-dimensional reproductions, transparencies, halftone plates, lithographic plates, masks,

grids, gratings, diffraction and interference slits, printing plates, printed circuits, pseudosilk-screen, etc.

The objects and advantages of the present invention will become apparent when the accompanying description of a few illustrative examples is read in conjunction with the annexed drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I schematically illustrates in sectional view an example of structural embodiment of a radiation-sensitive element according to the present invention;

FIG. 2 schematically illustrates in sectional view a modification of the radiation-sensitive element of FIG. 1;

FIGS. 3-5 schematically illustrate steps in obtaining a finished article according to a method of the present invention;

FIG. 6 schematically illustrates a modification of a finished article obtained according to a modification of the methods of FIGS. 3-5;

FIG. 7-12 schematically illustrate steps in further modifications of the method illustrated in FIGS. 3-5;

FIG. 13 is a schematic perspective view of a multilayer radiation-sensitive element according to a modification of the present invention, shown in a grossly exaggerated manner with respect to the thickness thereof, in the process of being exposed to electromagnetic radiation through an appropriate mask or screen;

FIG. 14 is a schematic representation in section of the arrangement of FIG. 13;

FIG. 15 is a view similar to FIG. 14, but showing the radiation-sensitive element after exposure to incident electromagnetic radiation;

FIG. 16 is a perspective schematic view of an example of finished article obtained from the radiation-sensitive element of FIG. 13 after exposure to electromagnetic radiation and removal of the radiation provoked interreaction product, according to an aspect of the present invention;

FIG. 17 is a sectional view of the article of FIG. 16;

FIG. 18 is a perspective schematic representation of another example of finished article obtained from the article of FIG. 16 by way of a further step in the process, according to another aspect of the present invention;

FIG. 19 is a sectional view of the article of FIG. 18;

FIG. 20 is a perspective schematic view of an example of an alternate resulting finished article;

FIG. 2] is a schematic sectional view illustrating a further aspect of the present invention;

FIG. 22 is a schematic sectional view of an article resulting from the method of FIG. 21;

FIG. 23 is a schematic representation of an arrangement according to the present invention for exposing a metallic surface to incident actinic radiation in the presence of a reacting material in a nonsolid form;

FIG. 24 is a schematic representation of an example of a finished article obtained by means of the method illustrated in FIG. 23;

F IG. 25 is a sectional view of a portion of the arrangement of FIG. 23 during exposure to incident electromagnetic radiation;

FIG. 26 is a view similar to FIG. 25 but showing a metallic plate, foil or thin-film after exposure to incident radiation;

FIG. 27 is a view similar to FIG. 26 but showing the finished article;

FIG. 28 is a view similar to FIG. 27 but showing a further variety of finished article;

FIG. 29 is a schematic view similar to FIG. 25 but showing another aspect of the methods of the present invention;

FIG. 30 is a schematic representation of the metallic plate, foil or thin-film after exposure to incident radiation according to the method of FIG. 29;

FIG. 31 is a schematic representation of an example of finished article obtained by the method of FIG. 29; and

FIG. 32 is a schematic representation of a modified finished article obtained according to the methods of a further aspect of the present invention.

DETAILED DESCRIPTION OF THE PREFERRITD EMBODIMENTS According to an aspect of the present invention, a selfrevealing radiation-sensitive element as generally shown at I0 in FIG. I is made by coating a metallic layer consisting of silicon, metal, metal alloy or a compound containing silicon or a metal as one of its constituents. and shown at I2, with an overlayer I4 of an inorganic material capable, when exposed to actinic electromagnetic radiation, of interreacting with the metallic layer I2 at the boundary l6 therebetween such as to cause a selective etching of the metallic layer which is, in depth, substantially proportional to the amount of actinic electromagnetic radiation impinging upon the sensitive element 10. By amount of actinic electromagnetic radiation is meant both the intensity of the radiating energy impinging upon the element and the duration of exposure of such element to the radiation. The in-depth etching effect upon the metallic layer 12 results from a radiation provoked interreaction between the material of the overlayer l4 and the metallic layer 12, with the formation of an interreaction product, or products, different in chemistry as well as in physical characteristics from either constituents.

Consequently, when an image is projected upon the surface of the radiation-sensitive element I0 by way, for example, of

an arrangement as schematically illustrated in FlG. 3, a screen 18 being disposed in the path of the incident radiation 20, the amount or intensity of the passing radiation 20 impinging upon the surface of the sensitive element, thus depends from the transmittance of the screen 18 to the incident radiation. If the screen 18 has portions, such as shown at 22, which are fully transmissive with respect to the incident radiation, full intensity passing radiation impinges upon the sensitive element 10 on portions corresponding to the fully transmissive portions 22 of the screen. Portions of the screen such as shown at 24, which are opaque to the incident radiation, prevent any radiation from reaching the sensitive element. Other portions, such as shown at 26, which have only partial transmissivity, substantially reduce the energy of the incident radiation passing therethrough, while other portions of the screen 18 may be such as, as shown at 28, to present more or less progressive transmissivity, such as to provide the full range of the socalled grey scale or any portion thereof.

While the sensitive element 10 is being exposed to the effect of incident radiation through screen I8, there is a radiation provoked interreaction taking place between the inorganic material of the overlayer I4 and the material of the metallic layer I2 at the borderline or interface 16 therebetween, such that, as shown in FIG. 4, there is formed at the interface a radiation provoked interreaction product, or products, generally designated at 30, such product or products including the constituents of both layers 12 and 14, causing a selective in-depth etching of the metallic layer 12, the depth of the etched portions being substantially proportional to the incident radiation energy impinging upon the sensitive element. Consequently, corresponding to the portions of screen 18 which are fully transmissive of the incident radiation, the indepth etching of the metallic layer i2 is at its maximum, for a given time of exposure, as shown at 32. The in-depth etching of the metallic layer 12 is substantially reduced in areas corresponding to the portions of the screen I8 having reduced transmissivity, as shown at 34, and the in-depth etching of the metallic layer 12, as shown at 36, varies proportionally, although not linearly, to the transmissivity of the screen 18 where its transmissivity varies from full transmissivity to full absorption.

It has been discovered that the interreaction product 30, and, when so desired, both the interreaction product and the nonreacted portions of the overlayer I4, may be removed by dissolution in an appropriate basic solution such as, for example, a 0.5 normal solution of sodium hydroxide, or alternately, an aqueous solution of sodium sulfide, preferably a saturated solution at C. It has also been found that the unreacted portions of the overlayer 14, together with the interreaction product 30, may be mechanically removed from the metallic layer 12 such as by wiping with a rag or, preferably, removal by means of a sheet of flexible material coated on one face with a pressure-sensitive adhesive which is applied against the surface of the overlayer 14 and which is thus used to remove the unreacted portions together with the interreaction product by simply peeling off. Alternately, the interreaction product and the nonreacted portions of the overlayer 14 may be removed by heat sublimation.

Whatever method is used for removing the nonreacted portions of the overlayer 14, together with the interreaction product 30, the finished article, as shown in FIG. 5, consists of the metallic layer 12 presenting on its surface which, before processing, constituted part of the boundary interface 16 between the metallic layer 12 and the overlayer 14, various indepth depressions as shown at 32, 34 and 36, defining a relief image with the depressions being of a depth corresponding to the amount of exposure of the sensitive element to radiation. It is evident that when the screen 18, shown in FIG. 3, is provided with only high contrast portions, and the radiation-sensitive element comprises a thin metallic layer 12 of the order of a few atom layers to a few mils in thickness, if the time of exposure of the sensitive element to the incident radiation is long enough, the interreaction between the overlayer 14 and the metallic layer 12 becomes such as to completely exhaust all the metal in the metallic layer 12 corresponding to the portions where the radiation provoked interreaction takes place, such that the finished article, as shown at FIG. 6, consists of the metallic layer 12 provided with perforations or through apertures, as shown at 38. In some applications the finished article of FIG. 6 may be used as such, or if it is desired to provide a support backing therefore, the metallic layer 12 may be ccmented or bonded to any appropriate backing material.

A list of elements particularly suitable for the metallic layer 12 includes, among others, silver, copper, lead, cadmium, zinc, iron, tin, arsenic, bismuth, cobalt, germanium, indium, manganese, mercury, nickel, selenium, silicon, tellurium, thallium, and vanadium. In other words, silicon and practically every metal has been found to be suitable, with the exception of substantially unactive metals, such as gold, rhodium, palladium and platinum. Aluminum and magnesium have also been found to be relatively unactive when used in the structure of the invention with an overlayer 14 of inorganic material of the type hereinafter disclosed. The metallic layer 12 is in the form of a thin foil of a thickness that may vary, according to the purpose to be accomplished and according to the proposed use of the sensitive element, from a few atom layers to a fraction of a mil or even to several mils. When using a very thin metallic layer which is substantially transparent," i.e., which has substantially good transmissivity to the actinic radiation, the sensitive element may be exposed by having incident radiation impinge upon the surface of the metallic layer 12 (FIG. 1) as well as having the radiation impinging upon the surface of the overlayer 14.

By metallic layer is meant herein a layer containing silicon or any one of the common metals hereinbefore mentioned, either alone, or alloyed to another common metal, or in the form of a metallic mixture. Consequently, the term metallic layer" as used herein means a layer of a material containing silicon or at least one metal in the form hereinbefore indicated.

The overlayer 14 is also substantially thin, of the order of a few atom layers to several microns, or even a few mils, and it may consist of any one of a variety of ternary and binary materials and compounds and any one of a few elements. An example of ternary material, which has been found to be particularly suitable, is a glassy material consisting of arsenic, sulfur and iodine for example in the following proportions: ar-

senic40 percent by weight, sulfur-50 percent by weight and iodine-l0 percent by weight, although the proportion of iodine may be within the range of l to 30 percent by weight. Appropriate examples of such ternary materials are given in U.S. Pat. No. 3,024,l l9, issued Mar. 6, I962. In such ternary materials, iodine may be replaced by chlorine, bromine, selenium, thallium or tellurium.

A multitude of binary compounds and mixtures have been found to be useful for the inorganic material of the overlayer 14. Examples of such binary compounds or mixtures comprise halides of metals, such as copper, antimony, arsenic, sulfur, thallium, lead, cadmium and silver, sulfides, arsenides, selenides, and tellurides of such metals. The most suitable materials, presenting substantial sensitivity when deposited on a metallic layer of copper, silver, lead, zinc, etc., for example, are arsenicsulfur mixtures and compounds, antimony-sulfur compounds and mixtures, silver-sulfur compounds and mixtures, bismuth-sulfur compounds and mixtures, chromium-sulfur compounds and mixtures, lead iodide, copper chloride, stannous chloride, mercury chloride, arsenic selenides, selenium-sulfur compounds and mixtures, chromium selenides, and indium-sulfur compounds. It seems that the property of reacting with a metallic layer under the influence of actinic electromagnetic radiation is shared by a variety of mixtures and compounds, having such property to varying but generally useful degrees. Such binary compounds and mixtures may be generally cataloged as consisting of a metal halide, or a mixture of a metal with a halogen, metal selenide, or a mixture of metal with selenium, metal sulfide, or a mixture of metal with sulfur, and metal telluride, or a mixture of a metal with tellurium. Stoichiometric proportions are not critical, but it is preferable that the resulting material be substantially transparent to electromagnetic actinic radiation of an appropriate wavelength, specially when the overlayer is substantially thick.

Single elements, such as halogens, selenium or sulfur, are also capable of reacting with a metallic layer when exposed to electromagnetic actinic radiation. Consequently, a general grouping of inorganic materials suitable as the material forming an actinically reactive overlayer when disposed on a metallic layer consists of halogens, sulfur, selenium, M-X compounds and mixtures and M-X-Y compounds and mixtures, wherein M is a metal and X and Y are selected from the group consisting of a halogen, sulfur selenium, and tellurium. The metal M is preferably selected from the group consisting of arsenic, antimony, bismuth, selenium, tellurium, copper, zinc, cadmium, mercury, lead, chromium, gallium, indium, thallium, germanium, tin, iron, cobalt, nickel and silver.

A particularly suitable binary material presenting substantial sensitivity when deposited on an appropriate metallic layer such as of silver or other metal is an arsenic-sulfur compound or mixture. For example, by using an overlayer 14 of arsenicsulfur deposited upon a metallic layer 12 of silver, the quality of the relief image obtained in the finished article is remarkable in its resolution. This is a very important quality when the finished article must present a high resolution as will be the case, for example, if the finished article is a diffraction grid or grating, or the like. The proportions of arsenic and sulfur may be varied broadly, such proportions preferably ranging from about 20 percent arsenic percent sulfur by weight to 80 percent arsenic20 percent sulfur by weight.

Structures of electromagnetic radiation-sensitive elements according to the present invention therefore consist principally of a metallic layer as defined herein provided with an overlayer of inorganic material capable of interreacting with the metallic layer when exposed to electromagnetic actinic radiation. The choice of the appropriate components for the diverse layers is a matter of judgment depending upon economic considerations relative to the cost of the components, the facility or difficulty of manufacturing the element, and the type and particular characteristics of the finished article to be obtained by the methods of the invention. As previously mentioned, silicon or any one of the metals hereinbefore listed as suitable for the metallic layer may be employed in combination with any one of the inorganic materials suitable for the overlayer.

The exact theory underlying the actinicly provoked interreaction between the material of the overlayer and the metalfur and 25 percent iodine, by weight. was heated to slightly above the temperature at which it becomes very liquid or fluidic, approximately 60 C. A sheet of silver, about 3 inches by 4 inches, was immersed in the fluidic mixture, removed and I 5 1 lic layer is not entirely known at the present, but it may be zi m vemcalflposmgnhto fa il f f fi postulated that the inorganic materials suitable for forming mlxmre to 0W0 e i owlllg f plateto the overlayer are dissociable when impinged upon by elecf fi izi g z s f" e coaungdo l tromagnetic actinic radiation in such a way that one or more f so l l t e Samp e was expose l g of the elements in the inorganic materials, upon actinic activa- 10 t: t l same manner as f fif i tion, are capable of chemically reacting with the adjacent respec Oexampe esame Swere metallic layer. It has been observed that the appropriate group EXAMPLE m of inorganic materials sultabie for making the overlayer in cooperation with silicon or an appropriate metal suitable for in r r o study the influence of varying ratios of conthe metallic layer may be selected according to certain physil5 stituents in arsenicsulfur-iodine mixtures, several samples of cal and chemical parameters which seem to be u eful in silver coating on a glass substrate where prepared. The samchoosing appropriate structures. As example of such parame- P r prepared by C nventional vacuum deposition ters, disassociation energy, heat of formation, and competitive t hniques by placing the glass substrates in a bell ar evacuoxidation reactions for silicon and metals seem to be involved a at bout 0.5 microns pressure. Silver metal was either individually or collectively. The following table. is a evaporated from tungsten electrical resistance heaters table of the respective heat of formation, expressed in kilo cal. brought to a out l, y h p age f electrical rr n per mol of the metallic compounds listed in the first vertical therethrough. By evaporating silver for about 3 onds, a column with the diverse metals listed in the upper horizontal i r ayer 11 h Substrate of about 4,000 A was Obtainedcolumn. it has been observed, as a result of the numerous tests Longer evaporation time provided proportionally thicker resulting in the discovery of the invention, that the preferable silver layers. For example, 15- to 20-second evaporation time metals for forming the metallic layer in cooperation with the provided silver layers on the glass substrate of approximately 1 inorganic materials of the overlayer of the invention are those micron. The thickness of the thin film of silver deposited on having a heat of formation below about 60 of the different sul-. the glass substrate was continuously monitored by a thin-film fides, chlorides, iodides, selenides, bromides and tellurides of thickness monitor such as manufactured by Edwards High the metal. The table seems to confirm the observed strong Va um Company. reactivity of silver and copper as compared to the relatively Several samples of radiation-sensitive element were weak reactivity of aluminum and magnesium. prepared by dipping the glass plates with a silver coating thus TABLE Fe Pb Ag Cu Ni Cd Al Mn Zn Cr Mg As Bi Go sumdt 23,06 22.2 5. 02 18.97 20.8 33. 93 126.4 47.3 45.88 s2. 20 19.1 43.3 1.35 tlllolitlu. l6.3ll 85.66 30.59 32. 50 74. {)8 02.99 166.8 112.7 99.54 99. 6-1 153.2 lodidc- 47. 55 41.84 14.93 15.8 41.62 48.38 71. 21 76.46 49. 70 54.2 86.74 Solonidu 10.1 12.4 0.956 7. 41 13.4 16.7 27 33. lilt'l1tlltlt.. 77.110 66.26 23.85 24.6 53.29 75. 7s) 12b.t1 90.8 77. 90 146.5 124.0 'lellnrid0 7.65 5.5 4.06 10.8 15.8 33. 21

EXAMPLE I obtained in various arsenic-sulfur-iodine mixtures to study the A I t i d b effect of various proportions of the constituents. It was found rd la we 5 was l e y 'ppmg a 45 that wide ranges of constituents permitted to obtain highly silver for] Into a dilute nitric acid solution for about 4 seconds reactive radiation sensitive elements when exposed to incident followed by rinsing 1n water. Thesurface of the silver for] was electromagnetic radiation. Various ratio mixtures were used, observed to turn to a frosted whitish coloration. The foil was f rom mixtures containing as little as 25 percent per weight of then dipped for a few seconds in a liquid arsenic-sulfur-lodme o o arsenic and as much as 40 percent of iodine, the balance being mixture heated to 60 C. and containing 40 percent ar- 50 senic 50 teem of Sulfur and m ercem of iodine b sulfur, to mixtures containing as much asbO percent of arsenic p8 P y and 50 percent of iodine, the balance being sulfur. weight. The foil was removed from the mixture and stood vertically to allow the excess arsemc-sulfur-todme mixture to drip EXAMPLE w off, thus leaving a thin layer of arsenic-sulfur-iodme material Upon the foil. The sensitive element thus obtained was then Several samples were prepared by utilizing an arseniculexposed to a high intensity light image being projected on one fur-iodine mixture containing 35 percent of arsenic, 40 pertace thereof, the light source for the image consisting of a 35- cent of sulfur and 25 percent of iodine, by weight. Diverse watt tungsten lamp whose filament image was focused on the metals were evaporated and condensed on glass substrates acsurface of the element. After about I minute of exposure time, cording to the process of example ill, substituting for the silver a stable self-revealed image of the filament appeared on the of example lll other common metals such as copper, cadmisensitive element. The exposed areas became dark brown urn, zinc, iron, lead, etc. while the unexposed areas of the element remained yellow in When exposed to electromagnetic actinic radiation such as color. The sensitive element was then rinsed in a 0.5 normal ordinary light, as previously explained, all of the samples solution of sodium hydroxide in order to remove or eliminate showed sensitivity to exposure to diverse degrees with remnants of the arsenic-sulfur-iodine film and byproducts pronounced etching of the metallic layer in depth all of the resulting from the interreaction between the arsenic-sulfurway to h glass substrate, f ff i exposure time d i in l and metal of the foil at the BxPosed areas, SllCh light intensity. Full etching all the way to the substrate was obas to obtain a relief etched image of the filament upon the surserved as a result f time exposures as short as three to 4 face of the foil. Mild aqueous solutions of sodium sulfide, amminutes for some metals such as silver, copper and iron, while monium hydroxide or potassium hydroxide may be used inless active metals required longer exposure time. stead of the sodium hydroxide solution.

EXAMPLE V EX MPLE ll A A silver for! was placed in a bell J31 evacuated at about 0.1 micron pressure. A quartz crucible located in an electrical re- A mixture consisting of 35 percent arsenic, 40 percent sulsistance heater disposed in the bell jar was loaded with pieces of arsenic trisulfide, AS253, the silver foil being located at about 6 inches from the quartz crucible. The arsenic trisulfide was heated in the crucible to about 350 to 400 C., and a thinfilm thereof was deposited on a surface of the silver foil by evaporating the arsenic trisulfide from the quartz crucible for about 30-40 seconds. Several samples were thus prepared, nd after removal from the bell jar, were handled in normal ambient light without any appearance of deterioration over a short period of time. Some of the samples were exposed to an intense white light pattern, utilizing a 35-watt incandescent lamp. After exposure for a few minutes, of the order to 3 to 4 minutes, an image of the lamp filament was obtained, after which the samples were subsequently washed in a 0.5 normal solution of sodium hydroxide in order to remove from the silver foil the unreacted portions of the arsenic trisulfide coating and the interreaction product. An etched image of the lamp filament was thus obtained on the silver foil.

Other samples were exposed through photographic negatives, which resulted in visible positive reproductions of the negative mask. After washing of the exposed samples in a 0.5 normal solution of sodium hydroxide, the images were found to be three-dimensional etch reproductions of the originals.

EXAMPLE VI A copper foil was coated with a thin-film of cuprous chloride by vapor deposition according to the same technique as disclosed with a respect to example V. The radiation-sensitive element thus obtained was exposed in the same manner as disclosed with respect to example V, although longer exposure times were required to obtain a visible image, such exposure times being of the order of minutes. The samples were washed in a 0.5 normal solution of sodium hydroxide for removing the coating of cuprous chloride and the interreaction product at the exposed areas, the resulting product being a copper foil having an etched three-dimensional image on the surface thereof.

EXAMPLE Vll Several samples were prepared of a thin metallic coating on a glass substrate, such samples being made of many common metals such as lead, zinc, iron, nickel, etc., in addition to silver and copper. The metallic coatings were vacuum deposited on a glass substrate by means of the techniques hereinbefore explained, the metals being obtained from a tungsten filament in contact with a small quantity of the metal, vaporized when the tungsten filament was connected across a source of electrical power. The samples were thin coated with a thin film of arsenic trisulfide vapor deposited also according to the techniques hereinbefore explained. Silicon and all the metals listed, when coated with a thin film of arsenic trisulfide, exhibited sensitivity to diverse degrees when exposed to actinic electromagnetic radiation such as intense light. For sufficient exposure times, the thin films of silicon or metal, of the order of 2,000 to 4,000 A. on the glass substrates, were etched in depth all the way to the glass substrates when the samples were washed in the 0.5 solution of sodium hydroxide. Some metals, such as aluminum and gold, were found to be relatively unaffected by exposure to incident light when coated with a thin film of arsenic trisulfide and further experiments using other coatings on such metals revealed that they remain unaffected by exposure to light.

EXAMPLE Vlll Several samples were prepared of an evaporated thin film silver coating on glass substrates according to the vacuum deposition technique hereinbefore explained. A mixture consisting of 60 percent arsenic and 40 percent sulfur, by weight, was placed in a quartz crucible in an electric resistance heater in a helljar evacuated to about 0.1 micron pressure. The silver on glass substrate samples were located about 6 inches from the quartz crucible and the arsenic-sulfur mixture was heated to about 350 C., thus evaporating the mixture. Film thicknesses of about 2 microns were obtained by evaporation of the mixture for about 40 seconds, and the samples were removed from the belljar and stored in a darkened area. Prior to storage, the samples were examined under normal roomlighting conditions and they were found to be gold in color on the coated silver surface.

The samples were then subjected to an intense white light pattern from a 35-watt illumination lamp having its filament focused on the sample for successive short periods of time with periodic inspections. The periodic inspections disclosed that the silver layer was being consumed in the areas impinged upon by the intense illumination, while those areas not subjected to illumination remained undisturbed. For total illumination periods of 3 to 4 minutes, the silver layer, where exposed to illumination, was entirely consumed in depth all the way to the glass substrate. Many samples were exposed through photographic transparencies and masks. It was found that the interreaction product of the exposed areas could be removed by simply wiping or brushing the surface of the samples, or, alternately, by applying to the surface of the arsenicsulfur coating a conventional adhesive tape and lifting the tape, the interreaction product at the exposed areas remaining adhering to the adhesive tape, while the portions of the overlayer corresponding to the unexposed areas remained strongly adhering to the metal overlayer when the tape was pulled. Some samples were prepared with the surface of the arsenicsulfur coating or overlayer covered with transparent tape. The samples were exposed, and by lifting the adhesive tape in the interreaction product at the exposed areas was removed without damaging the unexposed areas. in samples where it was desired to remove the remaining arsenic-sulfur coating so as to physically expose the metallic underlayer, mild alkaline solutions such as solutions of 10 percent of NH OH were used.

EXAMPLE [X A plurality of samples were prepared each consisting of a thin film of a different metal, deposited on a glass substrate according to the vacuum-deposition technique hereinbefore explained or consisting of a foil of the appropriate metal. The samples of diverse metal layers were coated with a vapordeposited arsenic-sulfur mixture evaporated from a crucible containing 60 percent of arsenic and 40 percent of sulfur, by weight, in the same manner and by the same methods as explained hereinbefore. The diverse metals were found to react with the material of the overlayer when exposed to electromagnetic actinic radiation such as intense white light, the samples being exposed as hereinbefore explained. Silicon and the diverse metals hereinbefore listed were found to be reactive in various degrees, the most reactive ones, in addition to silver and copper, being cadmium, lead, zinc and iron.

EXAMPLE X Samples consisting of an evaporated thin film of silver on a glass substrate were coated by the vacuum technique hereinbefore explained with arsenic-sulfur compounds and mixtures obtained from a boat disposed in a heater, a plurality of samples being prepared with various ratios of arsenic and sulfur placed in the evaporation boat, from mixtures containing as little as 20 percent of arsenic and as much as percent of sulfur, by weight, to percent of arsenic and 10 percent of sulfur, by weight. All of the samples were found to be remarkably sensitive to exposure to electromagnetic actinic radiation such as light, the variations in sensitivity being practically insignificant over the ratio range of the constituents.

EXAMPLE Xl A plurality of silver-coated glass plates were prepared according to the techniques hereinbefore explained. The silver layer was in turn coated, by way of the vacuum-deposition technique hereinbefore explained, with thin films of diverse inorganic materials comprising metal sulfides, metal iodides,

metal chlorides,.metal selenides, metal tellurides, arsenic-sulfur-halogen mixtures and other inorganic materials, such diverse inorganic materials being those listed hereinbefore. The samples exhibited reaction as a result of exposure to electromagnetic actinic reaction.

EXAMPLE XII A substrate of paper or cardboard was coated with a thin layer of silver about 1,500 A thick The vacuum-deposition technique hereinbefore explained was used for coating the paper with silver, although any known commercial process used for making metallized paper for the electronics industry, as well as the decorative paper industry, may be used. Following the coating of the paper with silver, :1 thin layer of cuprous chloride was evaporated upon the silver surface, using also the techniques hereinbefore explained,such overlayer of cuprous chloride being about 3,000 A thick Some samples were prepared by using lead iodide instead of cuprous chloride as a coating over the silver.

These samples were used as ordinary photographic contact paper and were exposed for periods of several minutes through photographic negatives, the duration of exposure de pending on the density of the negative and the source of light utilized. In the areas where light was transmitted to the photosensitive surface, a light induced photoreaction took place resulting in darkening of the surface to the point of turning black for sufficient exposure. After exposure, the samples were rinsed in warm tapwater. Altemately, a slight ammoniacal solution may be used instead of water. The immersing of the element in the water removed the unreacted overlayer material, thus fixing the image. The dark interreaction product remained attached to the silver coating forming a contrasting visual impression relatively to the silver background of the unreacted areas, resulting in photographic prints of high quality presenting all the conventional graduations in diverse degrees of the grey scale in the partly exposed areas.

Electromagnetic radiation-sensitive elements according to the present invention and provided with a substrate have a structure as schematically shown in cross section at FIG. 2. The radiation-sensitive element, generally designated at 11, and obtained according to any one of the processes hereinbefore explained in detail, comprises a substrate 40 which may be made of any one of many convenient materials such as glass, an epoxy resin, a fiberboard, a plastic, etc., on a face of which is disposed an adhering-metallic layer 12, placed on a surface of the substrate 40 by any convenient means such as being vapor deposited thereon as hereinbefore explained or cemented r bonded thereon, as shown at 42. Upon the metallic layer 12 is disposed another layer 14 of an inorganic material belonging to the class of materials mentioned hereinbefore. The sensitive element 11 of FIG. 2 is, for all purposes, similar in structure, operation and applications to the sensitive element of FIG. 1, the only difference being that the metallic layer 12 is generally much thinner than the metallic foil 12 of FIG. I and physical strength and rigidity are provided by the substrate or support backing 40 on which is disposed the metallic layer in adhesion therewith. When an image is projected, preferably upon the side provided with the overlayer I4, and when such image is of a variable density having a full range of "grey scale, corresponding self-revealing images are obtained, as precedently explained in detail, in all points similar to the relief image shown in FIG. 5, with the addition of a substrate or support backing being provided for the revealed metallic layer.

FIG. 7 represents an exploded view of an arrangement for exposing the radiation-sensitive element 11 through a mask or screen 18 having portions as shown at 22 substantially transmissive of the incident actinic radiation and having other portions, as shown generally at 24, capable of absorbing such incident radiation. In order to obtain a sharp image upon the surface of the sensitive element 11, it is best to have the screen 18 actually in contact with the surface of the overlayer 14, as diagrammatically illustrated in the cross-sectional view of FIG. 9, or, a lens system, not shown, may be used to project a sharp focused image upon the surface of the sensitive element, the lens system being such as to project either an enlarged or a reduced image, or, when so required, an image of the same size as provided on the screen 18. The incident radiation 20 passing through the transmissive portions 22 of the screen 18 impinges, as shown by arrows 20', upon the surface of the sensitive element 11. A shadow of the nontransmitting portions 24 of the screen is projected upon the surface of the sensitive element 11, as shown at 24 in FIG. 7. For illustrative purpose only, the shadow has been shown in the drawing as capital letters A and B of the alphabet. As previously explained hereinbefore and as illustrated in FIGS. 7 and 9, the transmitting portions 22 of the screen 18 permit the incident radiation to cause an interreaction between the inorganic material of the overlayer l4 and the silicon or metal of the metallic layer 12 which in turn causes a radiation-provoked etchlike action upon the metallic layer 12, with formation of an interreaction product as shown at 30 in FIG. 10, such that the radiationprovoked etching of the metallic layer 12 may be deep enough to reach the surface 42 of the support backing 40. By heat sublimation, or washing in water or in a mild alkaline solution, or by mechanical wiping, or, as previously explained also, by utilizing a flexible sheet of material, not shown, having on one surface thereof a pressure-sensitive adhesive, the interreaction product 30 can be removed, thus obtaining a finished article schematically represented in cross section at FIG. 11 wherein the support backing 40 is provided with an adhering etched metallic layer 12 still coated with an etched overlayer 14. Because the adherence of the overlayer 14 upon the metallic layer 12 at the interlayer boundary 16 thereof is generally less than the adherence of the metallic layer 12 to the support backing 40 at the interlayer boundary 42 therebetween, it is also quite feasible to remove, by washing in water or in a mild alkaline solution, or by mechanical means, both the interreaction product and the superficial overlayer 14 thus obtaining the finished article illustrated in FIG. 12 in schematic cross section and in FIG. 8 in perspective view. Such finished article consists of the support backing 40 and of the portions of the metallic layer 12 which have not been exposed to the influence of the incident radiation.

It is readily apparent that the invention permits relief reproduction of an image or engraving and is particularly useful for many applications, one of which constitutes a method of obtaining printed circuits by pseudophotographic means in a simple and low-cost manner. For so doing, the screen 18 of FIGS. 7 and 9 is simply an opaque drawing on a transparent support of the printed circuit to be reproduced, the support backing 40 of the sensitive element 11 consists of nonconductive material such as glass, fiberboard or a resin, and the finished article, similar to the article shown in FIG. 8, consists of a support backing 40 having strongly adhering thereon a metallic printed circuit of any thickness desired, depending upon the thickness of the metallic layer 12 of the sensitive element. It is evident that the screen 18 may consist of a transparent support for an opaque printed circuit drawing designed at any practical size and that the circuit board, the finished article, may be of any convenient size as obtained by means of a size-reducing projection lens system. Such a process leads naturally to any amount of miniaturization that may be desired.

Preparing printed circuits according to the methods of the invention compares favorably with any printed circuit board manufacturing processes, whether they are chemical processes such as the etched foil process, the screening processes, the photo methods and the like, that all require the use of resist compositions for coating the foil and the use of acid etchants, or whether they are the mechanical processes for making printed circuits such as the stamp wiring methods, the embossed wiring methods, the sprayed wiring methods, the molded wiring methods, the universal grid-wiring methods, which not only require a considerable amount of equipment to be practiced, but which also lead to many rejects.

in some printed circuit applications of the invention, it has been found desirable not to remove the interreaction product nor the nonreacted portions of the overlayer which form good electrical insulation. The printed circuits thus prepared are simply encapsulated in a material which is not light radiation transmissive or they are placed in a light-shielding enclosure.

It can thus be seen that the methods of the inventions lead to finished articles having many applications, as will be obvi ous to those skilled in the art, which compare very favorably with any conventional methods for obtaining such articles, and which are even simpler than ordinary photographic processes by requiring no complicated chemicals or conditions for processing of the plates, the finished article being actually the residue of the original materials which remains after exposure to appropriate radiation, the interreaction products resulting from the exposure being eliminated, contrary to other photographic processes where the residue is generally eliminated and the interreaction products are utilized in the finished article.

A multilayer radiation element can be made, according to the present invention, by superimposing a plurality of bilayer members, each comprising a metallic layer as herein defined and an overlayer of inorganic material capable of reacting with silicon or the metal of the metallic layer when exposed to appropriate electromagnetic actinic radiation. For example, referring more particularly to FIGS. 13l4 of the drawings, a multilayer radiation-sensitive element according to the present invention comprises a plurality of strata each consisting of a pair of substantially adhering layers 12 and 14 made of dissimilar materials. The multilayer radiation-sensitive element 10 may be disposed upon a support backing or substrate 40, although such support backing or substrate may be omitted in some applications.

In the example of the invention, illustrated at FIGS. 13-14, a radiation-sensitive element 10 is shown as consisting of three strata, each including a pair of layers 12 and 14 made of dissimilar materials capable of interreacting when exposed to electromagnetic radiation with the formation of a resulting interreaction product having chemical and physical characteristics different from the original constituents. As described in detail hereinbefore, each stratum comprises a'metallic layer 12, as defined herein, containing silicon or at least one metal, either alone, alloyed with another metal or with other metals, or combined or mixed with another element or other elements. Each metallic layer 12 may thus include silicon or any one of common metals such as silver, lead, nickel, copper, iron, etc., mentioned hereinbefore. The material of each layer 14 may be any one of the groups of ternary, binary or other materials, or any one ofa plurality of single elements, as mentioned hereinbefore.

Each layer 12 or 14 is substantially thin, and may have a thickness comprised between a few atom layers to several thousand Angstroms. As many strata or layer pairs as practical may be used in a radiation'sensitive element according to the present invention, the only condition being that each stratum be substantially transmissive of the actinic electromagnetic radiation used for exposure, such electromagnetic radiation being in many cases simply ordinary intense white light, such that the impinging radiation may reach substantially deeply to an appropriate stratum during exposure. Because there is a certain amount of absorption of the electromagnetic radiation at each layer, the depth of penetration of the electromagnetic radiation is substantially proportional to the irradiation intensity.

Exposure to electromagnetic radiation of a multilayer radiation-sensitive element according to the invention may be ef' fected by projection of an appropriate image upon the surface of the element, such exposure being represented at FIGS. 13 and 14 as being effected through a mask 18 having areas, such as shown at 22, which are substantially transmissive of the incident electromagnetic radiation arbitrarily represented by arrows 20, and other areas such as shown at 24, which are substantially nontransmissive of the electromagnetic radiation. Consequently, the electromagnetic radiation 20 is allowed to impinge selectively and discretely upon the radiation-sensitive element at appropriate areas 44 corresponding to the transmissive portions 22 of the mask or screen 18, while other areas 46 are shielded by the nontransmissive portions 24 of the screen and are not impinged upon by the radiation. At the areas 44 irradiated by the electromagnetic radiation 20, for sufficient intensity of the radiation energy, there is caused an in-depth penetration of the radiation as arbitrarily shown by arrows 20 with the result that the materials of the layers 12 and the layers 14 at the areas thus irradiated and penetrated interreact so as to form an interreaction product as shown at 30 in FIG. 15. The formation of such interreaction product causes a local decrease in the interlayer adhesion which permits mechanical removal of the radiation exposed portions of the element 10, according to the methods hereinbefore explained. Alternately, the interreaction product 30 is capable of selective removal by chemical means or by heat sublimation, as also explained hereinbefore.

A typical example of a multilayer radiation-sensitive element 10 according to the invention comprises a first metallic layer 12 made, for example, of silver vacuum deposited according to the techniques hereinbefore explained on a substrate 40 made of any appropriate convenient material such as paper, glass, plastic, metallic foil, or the like. The thickness of the metallic layer 12 is typically of a few atom layers to several Angstroms. On top of the first metallic layer 12 is deposited, for example, also according to the vacuum-deposited technique hereinbefore explained, a thin coating R4 of an inorganic material which when exposed to electromagnetic radiation interreacts with the silver of the metallic layer 12 For example, the coating or overlayer 14 consists of an arsenic-sulfur mixture or compound, preferably of the type which is substantially transmissive of the actinic electromagnetic radiation. Arsenic disulfide, trisulfide and pentasulfide are convenient materials in view of their glassy structure substantially transmissive of ordinary light, infrared radiation and the like. Typically, the thickness of the overlayer 14 is also of the order of a few atom layers to several microns. The first overlayer 14 is in turn provided with an adhering layer of a second metallic layer 12, in turn provided with an overlayer 14 of an appropriate inorganic material such as arsenic trisulfide or arsenic pentasulfide. As many strata, as desired, each consisting of a metallic layer 12 with an appropriate overlayer of inorganic material 14 are thus superimposed on top of each other by successive deposition operations. The resulting radiation sensitive element 10', FIGS. 1344, consists of a plurality of alternating thin metallic layers and inorganic layers, each thin enough to be substantially transmissive of electromagnetic radiation such as ordinary intense white light, such that, for appropriate radiation, the formation of interreaction product 30 is caused to extend in depth all the way through the whole thickness of the radiation-sensitive element 10, for appropriate exposure, such that, in the example shown herein which is provided with a support backing or substrate 40, for appropriate exposure, interreaction product is formed at the irradiated areas all the way to such support backing or substrate. The interreaction product 30 thus formed is also substantially transmissive of the electromagnetic radiation. Consequently, the formation of the interreaction product does not substantially impede the formation of further interreaction product at lower levels of the structure for adequate illumination. If so desired, the substrate 40 may be omitted and the diverse metallic layers 12 may be made of different metals, while the diverse layers 14 of inorganic materials may be made of different materials.

After removal of the interreaction product 30, there results a finished article 11, as shown in FIGS, 16 and 17, comprising voids 48 corresponding to the irradiated areas thereof, and portions such as shown at 50 and 52 corresponding to the areas having not been struck by the electromagnetic radiation.

If it is desired to obtain a finished article provided with a recessed representation of the contour of the image originally projected upon the radiation-sensitive element, the portions of the finished article 11 of FIGS. 16 and 17 included within the perimeter of such contour are removed by conventional mechanical means or by way of a subsequent exposure to electromagnetic radiation through an appropriate mask permitting the electromagnetic radiation to impinge upon appropriate areas, such as 50, in order to provoke the formation of interreaction product weakening the bond between layers thereof for facilitating mechanical removal thereof, or, alternately, permitting such interreaction product to be removed chemically or by heat sublimation. The resulting article 11' is as shown at FIGS. 18 and I9, and includes raised portions 52 corresponding to the unexposed areas and recessed portions such as shown at 54 defining a recessed representation of the original image.

If an opposite result is desired, the portions 52 of the article 11 of FIGS. 16 and 17 are removed, thus leaving, as shown at FIG. 20, an article 11" presenting a relief image 56 of the original image.

In view of the progressive absorption of the radiation transmitted in depth through the multiplelayers of a multilayer radiation-sensitive element according to the present invention, a'finished article provided with a relief image presenting a contour in depth substantially representative of the intensity of the electromagnetic radiation impinged thereupon may be obtained with an arrangement as schematically represented at FIG. 21. A radiation-sensitive element comprising several strata each including a pair of layers 12 and 14 of dissimilar materials capable of interreacting, as precedently explained, when irradiated, is exposed through a mask 18 presenting portions 24 nontransmissive of the incident electromagnetic radiation 20, portions 22 fully transmissive of the electromagnetic radiation and portions 28 partially transmissive of the electromagnetic radiation. Such portions 28 of the mask 18 are arbitrarily shown as having a gradual progressive increase of transmissivity of the radiation from the leftmost edge thereof, as seen in FIG. 21, to the rightmost edge, such that the radiation-provoked interreaction extends in depth within the radiation-sensitive element to a varied level, as shown at 36, substantially corresponding to the diverse boundaries between two consecutive layers at which enough radiation causes sufficient formation of interreaction product 30 to accomplish an effective result such as for example weakening the interlayer bond sufficiently to facilitate mechanical removal of the irradiated portions of the sensitive element.

The resulting article, as represented at FIG. 22, presents contoured recesses, such as shown at 36, extending in depth to the appropriate boundary between the diverse layers 12 and 14 reached by the electromagnetic radiation with sufficient intensity to provoke appropriate formation of the interreaction product.

Radiation-sensitive elements according to the present invention need not include the layer of interreacting inorganic material in a solid form as heretofore disclosed. For some applications it has been found preferable to utilize a plate of silicon or a metallic plate, foil or thimfilm without an overlayer of inorganic material in a solid form, the inorganic material being disposed in contact with the metallic layer in a liquid or vapor phase during exposure of the metallic layer to actinic radiation.

According to the invention, a useful article in the form of a relief image on, and integral with a silicon or a metallic surface, as shown at FIG. 24, can be obtained by disposing, as shown at H08. 23 and 25, a silicon or metaliic element in the form of a plate, foil, or thin-film 12 in contact with an inorganic material, as shown at 14, which is in a liquid or vapor phase, such as to provide substantial mobility to the material and intimate contact between the material and the metal or metals of the plate, foil or thin-film.

An image is projected upon the surface of the silicon or metallic element 12 by way, for example, of the arrangement of H65. 23 and 25, a screen 18 being disposed in the path of actinic incident radiation 20. The screen 18 has portions, as shown at 22, which are transparent to or transmissive of the incident radiation and portions, such as shown at 24, which are nontransmissive of the incident radiation. It is obvious that means may be utilized to project an image upon the surface of the silicon or metallic element 12 other than the one represented in the drawing, such as will provide optical en largement or reduction of an appropriate image which is sought to be reproduced in relief on the metallic element 12.

At the surface areas of the silicon or metallic element 12 which are impinged upon, discretely and selectively, by the electromagnetic radiation transmitted by the transmissive portions 22 of the mask 18, there is caused an interreaction between the inorganic material 14 and the silicon or metal or metals of the element 12. After exposure, the surface of the element 12 is thus discretely and selectively etched as a result of the formation thereon, at the areas impacted by the electromagnetic radiation, of recesses, as shown at 34 in FIG. 26 resulting from the formation of interreaction product 30 at such areas. The formation of the interreaction product causes a selective etching of the silicon or metallic surface corresponding in depth to the intensity and duration of exposure to the actinic electromagnetic radiation. Once the interreaction product 30 is removed from the silicon or metallic surface, the finished article, as shown in FIGS. 24 and 27, consists of the element 12, provided with a surface having a relief image 58 consisting of the portions, or areas, of the surface of the element left undisturbed as a result of having not been impinged upon by the electromagnetic radiation in the presence of the inorganic material 14 in a vapor of liquid phase. Such portions 58 project, from as little as a few atom layers to several thousand Angstroms, from the recessed surfaces 34 of the element 12, the recessed surfaces corresponding to the portions of the element which have been partially etched as a result of the interreaction between thesilicon or' metal or metals of the element 12 and the inorganic material 14 causing a superficiai etching of such recessed surfaces. If such superficial etching is allowed to continue, with sufficient exposure to electromagnetic radiation with enough intensity and duration to consume all of the silicon or metals or metal of the metallic element 12, these results a complete etching in depth of the element with surface to surface voids being formed, as a result of removing the interreaction product 30, such as shown at 38 on HO. 6, leaving a silicon or metallic pattern, as shown at 60, consisting of the portions of the element [2 having not entered into a reaction with the material 14 under the influence of the impinging actinic electromagnetic radiation.

lf instead of the mask, precedently described, comprising portions entirely nontransmissive of the incident electromagnetic radiation and portions fully transmissive of the electromagnetic radiation, a mask, substantially as shown at 18 at FIG. 29, is utilized, such mask being provided with portions 22 substantially fully transmissive of the incident radiation 20, portions 24 substantially nontransmissive of such radiation and portions 28 providing diverse degree of transmissivity to the electromagnetic radiation, and portions, such as shown at 26, which are partly transmissive of the electromagnetic radiation, there is formed on the element 12 after exposure a discrete and selective in-depth etching of the surface thereof, the depth of the etched portions being substantially proportional to the incident actinic radiation energy 20 impinging upon the element 12. There results a three-dimensional etching of the element 12 defining on the surface thereof etched depres sion resulting from the formation of the interreaction product 30. As shown at H6. 31, the element 12 is thus provided, after removal of the interreaction product 30, with portions etched in depth so as to correspond to the electromagnetic radiation energy having impinged upon the surface of element. Consequently, the element 12 is provided with substantially deeply etched portions 32 corresponding to the areas having been impinged upon by the greatest amount of radiation energy, with moderately etched areas 34, corresponding to the portions having received moderate irradiation, and with portions, as shown at 36, of varied depth representing a three-dimensional grey scale" rendition of the degree of irradiation of the surface.

As shown at FIG. 32, if the element 12 is provided with a substrate or support backing 40, for adequate exposure of portions of the element 12 to the incident radiation in the presence of an inorganic material 14 which is sufficient to etch all the way through such irradiated portions, the resulting finished article represents a structure having a relief pattern 60 adhering to the substrate or support backing 40.

As mentioned hereinbefore, the element 12 may include silicon or any one of the common metals, either alone, or as alloys, or as intermetallic compounds or in mixture.

The inorganic material 14 may be any one of the groups mentioned hereinbefore.

As an example of typical application of the method of the present invention, a silicon or metallic plate, foil, or thin-film is etched in a predetermined pattern according to the method hereinbefore described by disposing the plate, foil or thin-film in a vessel containing vapors of arsenic trisulfide, at a temperature of about 250 C. at atmospheric pressure. After exposure to an image projected thereon with ordinary white light for a duration of a fraction of a second to a few seconds, a slightly recessed planar reproduction of the image is obtained on the surface of the plate without further processing, as the interreaction product formed at the boundary between the surface of the plate and the arsenic trisulfide vapor is vaporized as soon as formed, as long as the surface temperature of the plate remains of the same order. A finished article can thus be obtained without further processing, and the relief image thus obtained can be preserved for an indefinite time without further precaution by simple removal from the atmosphere vapor-laden in arsenic trisulfide. Instead of arsenic trisulfide, any of the other inorganic materials hereinbefore mentioned may be used.

Operating at a lower temperature results in the surface of the plate being wetted with the reactant material such as arsenic trisulfide or the like being in a liquid phase, or alternately, the plate may be placed in a molten bath of the reactant material such as arsenic trisulfide or the like. With proper agitation and circulation of the bath, the interreaction product formed at the surface of the plate at the areas subjected to illumination, under appropriate conditions of proper flow, are carried away and remain in suspension or solution in the bath. The finished article emerging from the bath thus presents a relief image coated with a thin crystallized or glassy film of the reactant material adhering thereto which may be removed by appropriate mechanical means or which may be dissolved in a mild basic solution. Furthermore, any interreaction product that may remain adhering to the surface of the plate may also be soluble in such basic solutions. Alternately, also, if the temperature of the plate, when removed from the bath, is high enough to maintain the reactant material adhering to the surface thereof in a liquid phase, simple wiping cleans the plate dry and removes any interreaction product that may adhere thereto. lt is evident that by heating the plate, the interreaction product and any reactant material adhering thereto may thus be removed by sublimation.

In some applications, it may be advantageous to leave the interreaction product adhering to the plate surface so as, for example, to provide variable wettability of the surface or resistivity thereof for wet or electrostatic printing purposes, or for electronic purpose and in these cases precautions are taken so as to prevent the removal thereof.

Having thus described the invention by way of illustrative examples thereof, what is sought to be protected by United States Letters Patent is:

l. A method for making a plate element provided with a relief image on a layer of a first inorganic material disposed on a support backing, said method comprising: projecting an electromagnetic actinic radiation image upon an electromagnetic radiation-sensitive element having said support backing provided with said layer adhering thereto and an overlayer on said first layer of an inorganic second material different from that of said first layer and capable when exposed to said electromagnetic actinic radiation image to form an interreaction product therewith, wherein said first layer comprises at least one element selected from the group consisting of silver, copper, lead, cadmium, zinc, iron, tin, arsenic. bismuth, cobalt, germanium, indium, manganese, mercury, nickel, selenium, silicon, tellurium, thallium and vanadium, and said inorganic second material is selected from the group consist ing of sulfur, selenium, M-X compounds and mixtures and MXY compounds and mixtures wherein M is a metal selected from the group consisting of arsenic, antimony, bismuth, selenium, tellurium, copper, zinc, cadmium, mercury, lead, chromium, gallium, indium, thallium, germanium, tin, iron, cobalt, nickel and silver, and X and Y are selected from the group consisting of halogen, sulfur, selenium and tellurium, maintaining said plate element substantially at room temperature while projecting said electromagnetic actinic radiation image thereon, and removing said interreaction product thus leaving said relief image formed by portions of said first layer remaining adherent to said support backing.

2. The method of claim 1, wherein the formation of said interreaction product causes a selective etching of the metallic layer which extends in depth all the way through said metallic layer.

3. The method of claim 1, wherein said interreaction product is mechanically removed.

4. The method of claim 1, wherein said interreaction product is chemically removed.

5. The method of claim 1, wherein said interreaction product is removed by subsequent heat sublimation.

6. The method of claim 3, wherein the portions of said material which have not interreacted with the metal of said metallic layer are also mechanically removed.

7. The method of claim 4, wherein the portions of said material which have not interreacted with the metal of said metallic layer are also chemically removed.

8. The method of claim 5, wherein the portions of said material which have not interreacted with the metal of said metallic layer are also removed by heat sublimation.

9. The method of claim 1, comprising the additional step of disposing said element in an enclosure nontransmissive of said electromagnetic radiation.

10. A method for obtaining a relief image on a surface comprising: selectively and discretely impinging electromagnetic actinic radiation upon said surface in the presence of a vapor of an inorganic material difierent from that of said surface and capable of forming a radiation provoked interreaction product with said surface, wherein said surface comprises at least one element selected from the group consisting of silver, copper, lead, cadmium, zinc, iron, tin, arsenic, bismuth, cobalt, germanium, indium, manganese, mercury, nickel, selenium, silicon, tellurium, thallium and vanadium, and said inorganic material is selected from the group consisting of sulfur, selenium, M-X compounds and mixtures and MX-Y compounds and mixtures wherein M is a metal selected from the group consisting of arsenic, antimony, bismuth, selenium, tellurium, copper, zinc, cadmium, mercury, lead, chromium, gallium, indium, thallium, germanium, tin, iron, cobalt, nickel and silver, and X and Y are selected from the group consisting of halogen, sulfur, selenium and tellurium, and removing said interreaction product thus leaving said relief image formed by the unreacted portions of said surface.

11. The method of claim 10, wherein the formation of said interreaction product causes a selective etching of the metallic layer which extends in depth all the way through said metallic layer.

12. The method of claim 10, wherein said interreaction product is removed by chemical action.

13. The method of claim 12, wherein said interreaction product is dissolved in an aqueous solution of a base.

14. The method of claim 12, wherein said interreaction product is dissolved in an acid.

15. The method of claim 10, wherein said interreaction product is removed by mechanical action.

16. The method of claim 10, wherein said interreaction product is removed by heat sublimation.

17. A method for obtaining a relief image on a surface comprising: selectively and discretely impinging electromagnetic actinic radiation upon said surface in presence of an inorganic material different from that of said surface, said inorganic material being in a liquid phase and capable of forming a radiation-provoked interreaction product with said surface, wherein said surface comprises at least one element selected from the group consisting of silver, copper, lead, cadmium, zinc, iron, tin, arsenic, bismuth, cobalt, germanium, indium, manganese, mercury, nickel, selenium, silicon, tellurium, thallium and vanadium, and said inorganic material is selected from the group consisting of sulfur, selenium, M-X compounds and mixtures and M-XY compounds and mixtures wherein M is a metal selected from the group consisting of arsenic, antimony, bismuth, selenium, tellurium, copper, zinc, cadmium, mercury, lead, chromium, gallium, indium, thallium, germanium, tin, iron, cobalt, nickel and silver, and X and Y are selected from the group consisting of halogen, sulfur, selenium and tellurium, and removing said interreaction product thus leaving said relief image formed by the unreacted portions of said surface.

18. The method of claim 17, wherein the formation of said interreaction product causes a selective etching of the metallic layer which extends in depth all the way through said metallic layer.

19. The method of claim 17, wherein said interreaction product is removed by chemical action.

20. The method of claim 19, wherein said interreaction product is dissolved in an aqueous solution of a base.

21. The method of claim 19, wherein said interreaction product is dissolved in an acid.

22. The method of claim 17, wherein said interreaction product is removed by mechanical action.

23. The method of claim 17, wherein said interreaction product is removed by heat sublimation.

24. A method for making a relief image by means of a multilayer electromagnetic radiation-sensitive element comprising essentially a plurality of superimposed adhering strata substantially transmissive of said radiation, each one of said strata consisting of a pair of adhering layers made of dissimilar materials capable when exposed to actinic radiation to react with each other so as to form an interreaction product having a chemical composition and physical characteristics different from those of said layers prior to exposure to actinic radiation wherein one of said layers comprises at least one element selected from the group consisting of silver, copper, lead, cadmium, zinc iron, tin, arsenic, bismuth, cobalt, germanium, indium, manganese, mercury, nickel, selenium, silicon, tellurium, thallium and vanadium, and the second of said layer is an inorganic material selected from the group consisting of sulfur, selenium, M-X compounds and mixtures and M-XY compounds and mixtures, wherein M is a metal selected from the group consisting of arsenic, antimony, bismuth, selenium, tellurium, copper, zinc, cadmium, mercury, lead, chromium, gallium, indium, thallium, germanium, tin, iron, cobalt, nickel and silver, and X and Y are selected from the group consisting of halogen, sulfur, selenium, and tellurium, said method comprising the steps of: impinging an actinic radiation defined image upon the first of saidstrata such that said radiation partially penetrates selectively and discretely beyond the first of said strata to a depth proportional to the intensity of said radiation thus forming areas wherein said interreaction product is formed to a depth locally dependent from the intensity of said radiation; and removing said interreaction product. 25. The method of claim 24, wherein said radiation-defined image consists of an outline of the relief image to be obtained and comprising the additional step of:

removing at least one of said strata within the perimeter of said outline whereby a recessed surface is defined which corresponds to said outline. 26. The method of claim 24, wherein said radiation-defined image consists of an outline of the relief image to be obtained and comprising the additional step of:

removing at least one of said strata without the perimeter of said outline whereby a raised surface is defined which corresponds to said outline.

27. The method of claim 24, wherein said interreaction product is removed by selective chemical action.

28. The method of claim 24, wherein said interreaction product is removed by mechanical action.

29. The method of claim 24, wherein said interreaction product is removed by heat sublimation.

30. The method of claim 24, wherein the formation of said interreaction product causes a selective etching of the metallic layer which extends in depth all the way through at least one of said metallic layers.

31. A method for making a plate element provided with a relief image comprising: projecting an electromagnetic actinic radiation image upon an electromagnetic actinic radiation image upon an electromagnetic radiation-sensitive element consisting essentially of a pair of substantially adhering layers made of different inorganic materials capable when exposed to actinic radiation to form an interreaction product with each other, wherein one of said layers comprises at least one element selected from the group consisting of silver, copper, lead, cadmium, zinc, iron, tin, arsenic, bismuth, cobalt, germanium, indium, manganese, mercury, nickel, selenium, silicon, tellurium, thallium and vanadium, and the second of said layers is an inorganic material selected from the group consisting of sulfur, selenium, M-X compounds and mixtures and MXY compounds and mixtures, wherein M is a metal selected from the group consisting of arsenic, antimony, bismuth, selenium, tellurium, copper, zinc, cadmium, mercury, lead, chromium, gallium, indium, thallium, germanium, tin, iron, cobalt, nickel and silver, and X and Y are selected from the group consisting of halogen, sulfur, selenium and tellurium, maintaining said electromagnetic radiation element substantially at room temperature while projecting said electromagnetic actinic radiation image thereon, and removing said interreaction product and the unreacted portion of said second layer thus forming said relief image on said first layer.

32. The method of claim 31, wherein the formation of said interreaction product causes a selective etching of the metallic layer which extends in depth all the way through said metallic layer.

33. The method of claim 31, wherein said interreaction product and the unreacted portions of said overlayer are mechanically removed.

34. The method of claim 31, wherein said interreaction product and the unreacted portions of said overlayer are chemically removed.

35. The method of claim 31, wherein said interreaction product and the unreacted portions of said overlayer are removed by subsequent heat sublimation.

36. The method of claim 31, comprising the additional step of disposing said element in an enclosure nontransmissive of said electromagnetic radiation.

t a a: s

II-115 7; UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION v Patent No. 3,637,381 Dated J anuary'25 1972 Invent r(s) ROBERT w. HALLMAN ET AL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

IN THE SPECIFICATION Column 14, line3l, change "vacuum-deposited" to vacuum deposit ion 7 Column 16, line 42 before "results" change "these" to there I Q line 71 before "element" insert the IN CLAIMS v Column 20, I line 2 7, after "electromagnetic" cancel "actinic radiation" I I line 28, cancel "image upon an electromagnetic" In the list oflgeferences Cited Other Publications, i

change "Kost'yship" to Kostyshin v Signed and seal-ed this 5th 'day of September 1972.

(SEAL) Attest' EDWARD M.FLETCHER', JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents USCOMM-DC 603764 69 3* us, GOVERNMENT PRINTING OFFICE: I959 o-ase-saa ORM PO-105O (10-69) 

2. The method of claim 1, wherein the formation of said interreaction product causes a selective etching of the metallic layer which extends in depth all the way through said metallic layer.
 3. The method of claim 1, wherein said interreaction product is mechanically removed.
 4. The method of claim 1, wherein said interreaction product is chemically removed.
 5. The method of claim 1, wherein said interreaction product is removed by subsequent heat sublimation.
 6. The method of claim 3, wherein the portions of said material which have not interreacted with the metal of said metallic layer are also mechanically removed.
 7. The method of claim 4, wherein the portions of said material which have not interreacted with the metal of said metallic layer are also chemically removed.
 8. The method of claim 5, wherein the portions of said material which have not interreacted with the metal of said metallic layer are also removed by heat sublimation.
 9. The method of claim 1, comprising the additional step of disposing said element in an enclosure nontransmissive of said electromagnetic radiation.
 10. A method for obtaining a relief image on a surface coMprising: selectively and discretely impinging electromagnetic actinic radiation upon said surface in the presence of a vapor of an inorganic material different from that of said surface and capable of forming a radiation provoked interreaction product with said surface, wherein said surface comprises at least one element selected from the group consisting of silver, copper, lead, cadmium, zinc, iron, tin, arsenic, bismuth, cobalt, germanium, indium, manganese, mercury, nickel, selenium, silicon, tellurium, thallium and vanadium, and said inorganic material is selected from the group consisting of sulfur, selenium, M-X compounds and mixtures and M-X-Y compounds and mixtures wherein M is a metal selected from the group consisting of arsenic, antimony, bismuth, selenium, tellurium, copper, zinc, cadmium, mercury, lead, chromium, gallium, indium, thallium, germanium, tin, iron, cobalt, nickel and silver, and X and Y are selected from the group consisting of halogen, sulfur, selenium and tellurium, and removing said interreaction product thus leaving said relief image formed by the unreacted portions of said surface.
 11. The method of claim 10, wherein the formation of said interreaction product causes a selective etching of the metallic layer which extends in depth all the way through said metallic layer.
 12. The method of claim 10, wherein said interreaction product is removed by chemical action.
 13. The method of claim 12, wherein said interreaction product is dissolved in an aqueous solution of a base.
 14. The method of claim 12, wherein said interreaction product is dissolved in an acid.
 15. The method of claim 10, wherein said interreaction product is removed by mechanical action.
 16. The method of claim 10, wherein said interreaction product is removed by heat sublimation.
 17. A method for obtaining a relief image on a surface comprising: selectively and discretely impinging electromagnetic actinic radiation upon said surface in presence of an inorganic material different from that of said surface, said inorganic material being in a liquid phase and capable of forming a radiation-provoked interreaction product with said surface, wherein said surface comprises at least one element selected from the group consisting of silver, copper, lead, cadmium, zinc, iron, tin, arsenic, bismuth, cobalt, germanium, indium, manganese, mercury, nickel, selenium, silicon, tellurium, thallium and vanadium, and said inorganic material is selected from the group consisting of sulfur, selenium, M-X compounds and mixtures and M-X-Y compounds and mixtures wherein M is a metal selected from the group consisting of arsenic, antimony, bismuth, selenium, tellurium, copper, zinc, cadmium, mercury, lead, chromium, gallium, indium, thallium, germanium, tin, iron, cobalt, nickel and silver, and X and Y are selected from the group consisting of halogen, sulfur, selenium and tellurium, and removing said interreaction product thus leaving said relief image formed by the unreacted portions of said surface.
 18. The method of claim 17, wherein the formation of said interreaction product causes a selective etching of the metallic layer which extends in depth all the way through said metallic layer.
 19. The method of claim 17, wherein said interreaction product is removed by chemical action.
 20. The method of claim 19, wherein said interreaction product is dissolved in an aqueous solution of a base.
 21. The method of claim 19, wherein said interreaction product is dissolved in an acid.
 22. The method of claim 17, wherein said interreaction product is removed by mechanical action.
 23. The method of claim 17, wherein said interreaction product is removed by heat sublimation.
 24. A method for making a relief image by means of a multilayer electromagnetic radiation-sensitive element comprising essentially a plurality of superimposed adhering strata substantially transmissive of said radiation, each one of said straTa consisting of a pair of adhering layers made of dissimilar materials capable when exposed to actinic radiation to react with each other so as to form an interreaction product having a chemical composition and physical characteristics different from those of said layers prior to exposure to actinic radiation wherein one of said layers comprises at least one element selected from the group consisting of silver, copper, lead, cadmium, zinc iron, tin, arsenic, bismuth, cobalt, germanium, indium, manganese, mercury, nickel, selenium, silicon, tellurium, thallium and vanadium, and the second of said layer is an inorganic material selected from the group consisting of sulfur, selenium, M-X compounds and mixtures and M-X-Y compounds and mixtures, wherein M is a metal selected from the group consisting of arsenic, antimony, bismuth, selenium, tellurium, copper, zinc, cadmium, mercury, lead, chromium, gallium, indium, thallium, germanium, tin, iron, cobalt, nickel and silver, and X and Y are selected from the group consisting of halogen, sulfur, selenium, and tellurium, said method comprising the steps of: impinging an actinic radiation defined image upon the first of said strata such that said radiation partially penetrates selectively and discretely beyond the first of said strata to a depth proportional to the intensity of said radiation thus forming areas wherein said interreaction product is formed to a depth locally dependent from the intensity of said radiation; and removing said interreaction product.
 25. The method of claim 24, wherein said radiation-defined image consists of an outline of the relief image to be obtained and comprising the additional step of: removing at least one of said strata within the perimeter of said outline whereby a recessed surface is defined which corresponds to said outline.
 26. The method of claim 24, wherein said radiation-defined image consists of an outline of the relief image to be obtained and comprising the additional step of: removing at least one of said strata without the perimeter of said outline whereby a raised surface is defined which corresponds to said outline.
 27. The method of claim 24, wherein said interreaction product is removed by selective chemical action.
 28. The method of claim 24, wherein said interreaction product is removed by mechanical action.
 29. The method of claim 24, wherein said interreaction product is removed by heat sublimation.
 30. The method of claim 24, wherein the formation of said interreaction product causes a selective etching of the metallic layer which extends in depth all the way through at least one of said metallic layers.
 31. A method for making a plate element provided with a relief image comprising: projecting an electromagnetic actinic radiation image upon an electromagnetic actinic radiation image upon an electromagnetic radiation-sensitive element consisting essentially of a pair of substantially adhering layers made of different inorganic materials capable when exposed to actinic radiation to form an interreaction product with each other, wherein one of said layers comprises at least one element selected from the group consisting of silver, copper, lead, cadmium, zinc, iron, tin, arsenic, bismuth, cobalt, germanium, indium, manganese, mercury, nickel, selenium, silicon, tellurium, thallium and vanadium, and the second of said layers is an inorganic material selected from the group consisting of sulfur, selenium, M-X compounds and mixtures and M-X-Y compounds and mixtures, wherein M is a metal selected from the group consisting of arsenic, antimony, bismuth, selenium, tellurium, copper, zinc, cadmium, mercury, lead, chromium, gallium, indium, thallium, germanium, tin, iron, cobalt, nickel and silver, and X and Y are selected from the group consisting of halogen, sulfur, selenium and tellurium, maintaining said electromagnetic radiation element substantially at room temperature while projecting said electromaGnetic actinic radiation image thereon, and removing said interreaction product and the unreacted portion of said second layer thus forming said relief image on said first layer.
 32. The method of claim 31, wherein the formation of said interreaction product causes a selective etching of the metallic layer which extends in depth all the way through said metallic layer.
 33. The method of claim 31, wherein said interreaction product and the unreacted portions of said overlayer are mechanically removed.
 34. The method of claim 31, wherein said interreaction product and the unreacted portions of said overlayer are chemically removed.
 35. The method of claim 31, wherein said interreaction product and the unreacted portions of said overlayer are removed by subsequent heat sublimation.
 36. The method of claim 31, comprising the additional step of disposing said element in an enclosure nontransmissive of said electromagnetic radiation. 